The overall goal of this proposal is to advance the understanding of the genetic signals that lead to development of cardiac muscle. The genetic program leading to skeletal muscle differentiation has been well described, and is dependent on the MyoD family of transcription factors. The sequence of events leading to cardiac muscle differentiation remains largely unknown, though cardiac muscle and skeletal muscle express overlapping muscle-specific genes. We hypothesize that transcription factors will guide cardiac muscle development, similar to the MyoD family's role in skeletal muscle differentiation. The homeobox genes are likely involved in cardiac muscle development, since they play a prominent role in mesodermal development in multiple species. A Drosophila homeobox gene, tinman, is essential for early cardiac development since a homozygous tinman null mutant does not develop a dorsal vessel, the Drosophila heart analogue. The murine homologue of tinman, Csx, was cloned in my sponsor's laboratory. Preliminary analysis indicates expression during early murine cardiac development before other muscle-specific genes are expressed. In addition, although homozygous Csx null mice do develop a heart tube, the cardiac morphology is clearly abnormal. Mutations in or loss of function of Csx seem to fundamentally alter development of cardiac muscle and cardiac morphology as well. Our goal is to characterize the control of expression of Csx and its role in cardiac myocyte development by identifying the complete genomic structure of Csx, including the Csx promoter region. In vitro and in vivo, we will begin to define the regulatory elements involved in Csx expression. Overexpression of Csx in transgenic mice will allow further analysis of the effect of perturbations of Csx expression. We will also examine the expression pattern and chromosomal location of hCsx, the human homologue of murine Csx. As a pediatric cardiologist, I have a particular interest in the genetic pathways that lead to normal cardiac development. I began molecular biology research during my fellowship training, and am dedicated to pursuing an independent investigative career within the area of cardiac development. The sponsor, Dr. Seigo Izumo, Chief of Cardiology at the University of Michigan, is recognized for his work on transcription factors and cardiac gene expression. Dr. Izumo will provide the scientific guidance and training required to achieve my goal. His laboratory provides the necessary personnel and facilities to obtain research training in molecular biology. Furthermore. the University of Michigan is an active center for molecular biology research, in particular in relating molecular advances to medical practice, and provides a stimulating research environment in which to learn. It is an environment in which I expect to be able to acquire additional research skills to ultimately improve the understanding of the pathogenesis of congenital heart disease.